1. Field of the Invention
The present invention relates to an image data conversion process used in an image forming process and, more specifically to an image data conversion apparatus, an image data forming apparatus, and image data conversion method and program for improving visibility of an image that contains an achromatic color.
2. Description of the Related Art
When reading a source document using a digital color Multi Function Peripheral (MFP) or an image reading apparatus and forming an image data, image processing such as a color conversion process, or a filtering process is applied to an image data acquired from reading means such as CCDs or CISs. At this time, when focusing on an achromatic pixel area such as a black character in the source document, in the read image data, values of a red signal, a green signal and a blue signal (hereinafter referred to as RGB signals) are not necessarily the same.
In general, the image reading apparatus executes the filtering process for the RGB signals after having applied with the color conversion process. At this time, the strength of the filter is generally equalized for the respective RGB signals. Assuming that the sharpness in a specific signal is low in a device such as CCDs or CISs, the filter strength may be increased for a specific signal. However, when the filter strength is too strong, the balance of the RGB signals is disrupted in the black part, and hence when the image is displayed, the black part may appear on a display as if it slightly contains a color.
When printing the image data including a black pixel in which the balance of RGB signals is disrupted as described above, since the RGB data values of the pixels in the black part are not equal, the image is not necessarily formed only with black toner when forming the image.
In other words, in the image forming apparatus, the portion of black pixels in which the balance of RGB signals is disrupted as described above may be printed as a mixed color in CMYK. At this time, in the image forming apparatus, a disadvantage such that a color is viewed on a contour of a character due to misalignment of transfer positions of each toner in CMYK may often occur. There arises a problem such that the black character appears in a slightly different color from the achromatic color when the electronic data is printed due to CMY color toner being mixed therein, whereby the visibility is significantly lowered.